Work out sharding key distribution instantly with clear inputs, formula shown and shareable results.
Capacity in a sharded system is set by the hottest shard, not the average. The skew factor is the busiest shard's traffic share divided by the even share of 1/N, so 18 percent across 16 shards is nearly three times skew — meaning the cluster must be provisioned as if it were three times smaller. Skew usually comes from a low-cardinality or naturally hot key.
Shard skew
even share = 1 / shards; skew factor = hottest share / even share; hottest shard load = total rate x hottest share
Choose a higher-cardinality shard key, add a salt or bucket suffix to hot keys, or split the hot key's data across shards with a scatter-gather read.
It solves rebalancing on shard changes, not popularity skew. A single extremely popular key still lands on one shard however the ring is arranged.